1. Field of the Invention
The present invention relates to a photoelectric converting apparatus including a sensor unit and a memory unit.
2. Related Background Art
As one of conventional amplification type photoelectric converting apparatuses having sensor units, transfer units, and memory units, a CMOS inverting amplifier type sensor has been proposed in Japanese Patent Application Laid-open No. 09-200629, for example. The circuit arrangement of this conventional sensor apparatus is shown in FIG. 1. In this drawing, reference numeral 1 denotes a PN photodiode for performing a photoelectric converting (transfer) operation; 2, an amplifying MOS transistor for constituting an inverting amplifier; 3, a switch MOS transistor for supplying an output derived from a pixel to a vertical signal line 28; and 4, a resetting MOS transistor for resetting a potential of the photodiode. These circuit elements 1 to 4 constitute one pixel 5. Also, reference numeral 6 denotes a load MOS transistor of the inverting amplifier, and this load MOS transistor 6 is provided every vertical line. Reference numeral 7 denotes a transfer gate used to transfer pulses φSL1 and φPS1 which are employed to drive the respective pixels. The transfer gate 7 is controlled by a vertical scanning circuit 8. These circuit elements 1 to 8 constitute a sensor unit. Also, reference numeral 9 denotes a switch MOS transistor for entering an output signal derived from a pixel of the sensor unit into a transfer unit; 10, a clamp capacitance; and 11, another switch MOS transistor for entering thereinto a clamp potential VGR. Reference numeral 12 denotes an amplifying MOS transistor of a source follower; 13, a constant current source of the source follower; 14, a switch MOS transistor for feeding back an output derived from a clamp circuit to a pixel of the sensor unit; 15, a switch MOS transistor for entering an output derived from a memory circuit to the clamp circuit; and 16, another switch MOS transistor for supplying an output signal derived from the clamp circuit to a memory pixel 21. These circuit elements 10 to 13 constitute the clamp circuit used to eliminate noise. Furthermore, the circuit elements 9 to 16 constitute the transfer unit. Also, reference numeral 17 denotes a memory capacitance; 18, an amplifying MOS transistor of the inverting amplifier; 19, a switch MOS transistor used to read an output signal derived from the memory pixel to the vertical signal line; and 20, another switch MOS transistor used to enter an output derived from a pixel of the sensor unit, or from the transfer unit into the memory capacitance. These circuit elements 17 to 20 constitute a memory. Reference numeral 23 denotes a transfer gate for transferring memory drive pulses φPS2 and φSL2, and this transfer gate 23 is driven by a vertical scanning circuit 24. Also, reference numeral 22 denotes a load MOS transistor of the inverting amplifier, and a single load MOS transistor 22 is provided every column. These circuit elements 17 to 24 constitute the memory unit.
Reference numeral 25 denotes a horizontal selection MOS switch. The horizontal selection MOS switch 25 is controlled by a horizontal scanning circuit 26 in such a manner that the output signals derived from the respective memory cells are outputted via an output amplifier 27 to an external circuit in a serial form.
In this conventional CMOS inverting amplifier type sensor, as to the pixel cell of the sensor unit and the memory of the memory unit, since the circuits for constituting the inverting amplifiers are completely identical to each other, these inverting amplifier circuits are designed by employing the same parameters (for example, L, W, COX of MOS transistor). However, the gain of the inverting amplifier for the pixels of the sensor unit is equal to that of the inverting amplifier for the memory of the memory unit under such a condition that the circuits of the above-mentioned conventional sensor are not operated. As a result, this conventional sensor owns the below-mentioned drawbacks.
That is, in the case that the conventional sensor circuit is actually operated, since the gain of the signal outputted from the pixel of the sensor unit is different from that of the signal outputted from the memory of the memory unit, noise cannot be correctly removed.
It should be noted that a gain obtained under such a condition that the circuit is not operated will be referred to as a “DC gain”, whereas another gain obtained under such a state that the circuit is actually operated will be referred to as an “AC gain” in the below-mentioned description.
Also, for example, when the conventional photoelectric converting apparatus is employed as an auto-focus (AF) sensor of a single-lens reflex camera, there are other drawbacks that precision of an AGC (automatic gain control) circuit and also precision achieved under low brightness photographic condition would be deteriorated.